TS--is this normal?

[jasonober]

I just built a TS today using this:

http://www.generalguitargadgets.com/diagrams/ts_lo_808.gif


Signal passes through the circuit but the drive pot seems to have little effect (almost no overdrive).   Level and tone are effecting signal.


Readings are
9v supply--10.67
IC:
1.     2.59
2.    2.59
3.    2.61
4.    2.59
5.      0
6.   2.58
7.    2.58
8.    10.65


Q1(2N3904):
C.   10.67
B.     1.44
E.     1.33

Q2(2n3904)
C.   10.65
B.     1.51
C.     1.45

I'e checked all component values and they are right.   Other than that the only thing i don't know is if I orientated the .22uf tant. caps as orientation isn't indicated on layout.   Any suggestions?    I read GEO tubescreamer technology but I'm not sure what I'm missing.

[dosmun]

I would double check the Drive pot connections.

[Doug_H]

I just built a TS today using this:

http://www.generalguitargadgets.com/diagrams/ts_lo_808.gif


Signal passes through the circuit but the drive pot seems to have little effect (almost no overdrive).   Level and tone are effecting signal.


Readings are
9v supply--10.67
IC:
1.     2.59
2.    2.59
3.    2.61
4.    2.59
5.      0
6.   2.58
7.    2.58
8.    10.65


Q1(2N3904):
C.   10.67
B.     1.44
E.     1.33

Q2(2n3904)
C.   10.65
B.     1.51
C.     1.45

I'e checked all component values and they are right.   Other than that the only thing i don't know is if I orientated the .22uf tant. caps as orientation isn't indicated on layout.   Any suggestions?    I read GEO tubescreamer technology but I'm not sure what I'm missing.

First off, pin 4 of your IC should be grounded, so it should read 0v.

Pin 3 and Pin 5 should be sitting at roughly 1/2 of VCC, 4-5V.

Re-check your IC numbering again, if pin 5 is really 0v, that's a major problem.

I could be wrong but I would think the Q1, Q2 emitters should be sitting around 4-5V too.

Check the transistor pinouts and make sure you have the IC oriented correctly.

Double check your Vr rail and make sure it is around 4-5V too. If that is wrong, it will explain why the IC and transistors are not biased correctly.

Just some things to check out,

Doug

[petemoore]

The opamp pins, except Gnd and V+, should be around 40-60% of supply voltage, or near half of supply...10.65 X .5 = around 5.15V...so the Opamp is misbiased, in this case, pin 5 is at zero...
 Pin 4 is Ground, ground is not connected to this pin.

[jasonober]

so i guess i was tired   here's what i've got today(same PS different outlet)

voltage supply--------11.18

IC
1.       2.69
2.    2.78
3.       2.65
4.       0
5.      2.68
6.        2.68
7.       2.68
8.       11.15

Q1
C.    11.16
B.      1.5
E.    1.45


Q2
C.      11.15
B.        1.53
E.        1.45

Double check your Vr rail and make sure it is around 4-5V too. If that is wrong, it will explain why the IC and transistors are not biased correctly

when comparing the schematic
http://www.generalguitargadgets.com/diagrams/ts-808_sc.gif
and the layout
http://www.generalguitargadgets.com/diagrams/ts_lo_808.gif
i'm not sure which rail is Vr  can someone please clarify

[Doug_H]

i'm not sure which rail is Vr  can someone please clarify

It's the junctiion between R9, R10, & C7.

Doug

[jasonober]

thanks Doug

my Vr rail is showing 11.15 into the board from DC jack 2.69 after R9(10k) and then 2.69 across Vr until it goes through R2(510k) where it is now 1.5 into Q1 base.  Is R9 dropping this voltage too much?

[Doug_H]

thanks Doug

my Vr rail is showing 11.15 into the board from DC jack 2.69 after R9(10k) and then 2.69 across Vr until it goes through R2(510k) where it is now 1.5 into Q1 base.  Is R9 dropping this voltage too much?

Double check your R9, R10 values. Something is not right. Pull the resistors and check them with a meter to be sure.

Doug

[jasonober]

Double check your R9, R10 values. Something is not right. Pull the resistors and check them with a meter to be sure.

pulled r9 and r10   their value is correct 10K   replaced with 2.2 K

New readings:


voltage supply--------10.77

IC
1. 4.34
2. 4.38
3. 4.32
4. 0
5. 4.34
6. 4.35
7. 4.35
8. 10.77

Q1
C. 10.77
B. 2.36
E. 2.58


Q2
C. 10.74
B. 2.4
E. 2.64



I guess IC voltages are in a workable range but transistor still off.  any suggestions?

[jasonober]

will adjusting value or R2 & R3 for   Q1 and    R12 & R14-15 for Q2 help or am I missing something?

[Doug_H]

pulled r9 and r10   their value is correct 10K   replaced with 2.2 K

Okay, if one of the resistors is 10k and the other 2.2k and you are getting roughly 1/2 Vcc, you have another problem somewhere else.

Doug

[jasonober]

if one of the resistors is 10k and the other 2.2k and you are getting roughly 1/2 Vcc, you have another problem somewhere else.

sorry    i was unclear    I replaced both 10k resistors with 2.2k to get these voltages on IC.   Any ideas of what could be wrong elsewhere?
Would it help to have voltage readings form other places?

[Doug_H]

sorry    i was unclear    I replaced both 10k resistors with 2.2k to get these voltages on IC.   Any ideas of what could be wrong elsewhere?
Would it help to have voltage readings form other places?

Okay, now pull and check with DVM the resistor going from R9 & R10 to pin 3 of the op amp. Those resistors should not need to be so low. 10k should work fine.

doug

[jasonober]

WORKS!!!   Just starting pulling and measuring resistors and found a STUPID mistake with R6  i'd looked at this board for two days and finally realized it wasn't tied to ground.  Thanks for your help!

[Doug_H]

WORKS!!!   Just starting pulling and measuring resistors and found a STUPID mistake with R6  i'd looked at this board for two days and finally realized it wasn't tied to ground.  Thanks for your help!

Cool! Glad you got it working!

Make sure you re-install the 10k's for R9 & R10. That will help preserve the battery life.

Doug

[moeburn]

WORKS!!!   Just starting pulling and measuring resistors and found a STUPID mistake with R6  i'd looked at this board for two days and finally realized it wasn't tied to ground.  Thanks for your help!

I'm having the same problem you're having, my voltage divider won't give 4.5v unless the resistor ratio is wrong.  You said R6 should be tied to ground?  Schematic says it should be tied to Vr.  Either one doesn't work for me.